Exhaust Gas Heat Exchange for Ammonia Evaporation Using a Heat Pipe

ABSTRACT

A heat pipe has a first portion positioned within an exhaust path of a gas turbine exhaust processing system and a second portion positioned in a heat exchange relationship with a flow path of a heat exchange fluid. The flow path of the heat exchange fluid includes an ammonia evaporator configured to evaporate ammonia received from an ammonia source. The heat pipe is configured to transfer thermal energy from exhaust gas in the exhaust path to the heat exchange fluid to enable the heat exchange fluid to vaporize the ammonia while cooling the exhaust gas to enable the gas turbine exhaust processing system to more effectively process the exhaust gas.

BACKGROUND OF THE INVENTION

The subject matter disclosed herein relates to turbine systems and, morespecifically, to systems and methods for injecting cooling air intoexhaust gas flow(s) produced by turbine systems.

Gas turbine systems typically include at least one gas turbine enginehaving a compressor, a combustor, and a turbine. The combustor isconfigured to combust a mixture of fuel and compressed air to generatehot combustion gases, which, in turn, drive blades of the turbine.Exhaust gas produced by the gas turbine engine may include certainbyproducts, such as nitrogen oxides (NO_(x)), sulfur oxides (SO_(x)),carbon oxides (CO_(x)), and unburned hydrocarbons.

BRIEF DESCRIPTION OF THE INVENTION

In one embodiment, a gas turbine system includes an exhaust processingsystem fluidly coupled to an outlet of a turbine of a gas turbineengine, the exhaust processing system being configured to receive anexhaust gas having products of combustion generated by the gas turbineengine, and to process the exhaust gas before the exhaust gas exits thegas turbine system; an exhaust path of the exhaust processing systemconfigured to flow the exhaust gas through the exhaust processingsystem. The system also includes an ammonia injection system having asource of ammonia and configured to introduce vaporized ammonia into theexhaust path; and a heat pipe having a first portion positioned withinthe exhaust path and a second portion positioned in a heat exchangerelationship with a flow path of a heat exchange fluid used in theammonia injection system. The heat pipe is configured to transferthermal energy from exhaust gas in the exhaust path to the heat exchangefluid to enable the heat exchange fluid to vaporize the ammonia whilecooling the exhaust gas to enable the exhaust processing system to moreeffectively process the exhaust gas.

In another embodiment, a heat pipe has a first portion positioned withinan exhaust path of a gas turbine exhaust processing system and a secondportion positioned in a heat exchange relationship with a flow path of aheat exchange fluid. The flow path of the heat exchange fluid includesan ammonia evaporator configured to evaporate ammonia received from anammonia source. The heat pipe is configured to transfer thermal energyfrom exhaust gas in the exhaust path to the heat exchange fluid toenable the heat exchange fluid to vaporize the ammonia while cooling theexhaust gas to enable the gas turbine exhaust processing system to moreeffectively process the exhaust gas.

In a further embodiment, a gas turbine system includes a gas turbineengine configured to combust a mixture of fuel and an oxidant and torelease exhaust gas resulting from the combustion; an exhaust processingsystem having an exhaust duct fluidly coupled to an outlet of a turbineof the gas turbine engine, the exhaust duct being configured to receivethe exhaust gas released by the gas turbine engine. The exhaustprocessing system is configured to process the exhaust gas using aselective catalytic reduction (SCR) catalyst to reduce NO_(x) in theexhaust gas before the exhaust gas exits the gas turbine system. Anexhaust path of the exhaust processing system is configured to flow theexhaust gas through the exhaust processing system. An ammonia injectionsystem has an ammonia evaporator configured to receive aqueous ammoniafrom an ammonia source and vaporizes ammonia in the aqueous ammonia toenable the ammonia injection system to introduce vaporized ammonia intothe exhaust path. A plurality of heat pipes is configured to receivethermal energy from exhaust gas in the exhaust duct to cool the exhaustgas before the exhaust gas reaches the SCR catalyst, transfers thethermal energy to a heat exchange fluid used in the ammonia evaporatorto vaporize the ammonia.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 illustrates a diagrammatical overview of an embodiment of a gasturbine system having an exhaust processing system that uses heat pipesfor exhaust gas cooling and ammonia evaporation;

FIG. 2 illustrates a side elevational view of an embodiment of the gasturbine system of FIG. 1 in which the heat pipes have a first portionpositioned in an exhaust duct and a second portion positioned in anambient air heat exchanger;

FIG. 3 illustrates a schematic side elevational view of an embodiment ofthe exhaust processing system of FIG. 1 in which an exhaust processingcontrol system controls the flow of ambient air and the flow of aqueousammonia to achieve levels of ammonia evaporation suitable for use in theexhaust processing system;

FIG. 4 illustrates a cross-sectional view of an embodiment of the heatexchange configuration of the heat pipes in accordance with variousconfigurations of the present disclosure; and

FIG. 5 illustrates a schematic side elevational view of anotherembodiment of the exhaust processing system of FIG. 1 in which the heatpipes are used to directly vaporize ammonia.

DETAILED DESCRIPTION OF THE INVENTION

One or more specific embodiments of the present invention will bedescribed below. In an effort to provide a concise description of theseembodiments, all features of an actual implementation may not bedescribed in the specification. It should be appreciated that in thedevelopment of any such actual implementation, as in any engineering ordesign project, numerous implementation-specific decisions must be madeto achieve the developers' specific goals, such as compliance withsystem-related and business-related constraints, which may vary from oneimplementation to another. Moreover, it should be appreciated that sucha development effort might be complex and time consuming, but wouldnevertheless be a routine undertaking of design, fabrication, andmanufacture for those of ordinary skill having the benefit of thisdisclosure.

When introducing elements of various embodiments of the presentinvention, the articles “a,” “an,” “the,” and “said” are intended tomean that there are one or more of the elements. The terms “comprising,”“including,” and “having” are intended to be inclusive and mean thatthere may be additional elements other than the listed elements.

As set forth above, gas turbine engines may produce a number of productsof combustion. These products may include nitrogen oxides (NO_(x)),sulfur oxides (SO_(x)), carbon oxides (CO_(x)), and unburnedhydrocarbons. Generally, reducing the relative concentration of theseproducts within an exhaust gas may include reacting such products withother reactants in the presence of a catalyst. The reaction betweenNO_(x) and a reductant such as ammonia (NH₃), for example, may occurwithin an exhaust duct in the presence of a metal oxide catalyst of aselective catalytic reduction (SCR) system. The catalyst lowers theactivation energy of a reaction between the NO_(x) and ammonia toproduce nitrogen gas (N₂) and water (H₂O), thereby reducing the amountof NO_(x) in the exhaust gas before the exhaust gas is released from thegas turbine system. Such catalyst systems may be referred to as“DeNO_(x)” systems.

SCR systems may be used in a variety of different gas turbine systems,which range from relatively small scale systems to larger, heavy-dutygas turbine systems. Small scale systems produce exhaust gases having arelatively low temperature, while heavy-duty gas turbine systems produceexhaust gases with much higher temperatures. While exhaust gases fromsmall scale systems (e.g., aero-derivative systems) have a temperaturerange that is generally amenable to the SCR process, the temperature ofexhaust gases produced by heavy-duty systems is often much higher thanacceptable operating ranges for the SCR process (e.g., temperaturessuitable to maintain stability of the SCR catalyst). For example, inaccordance with an embodiment of the present disclosure, the isothermtemperature of exhaust gases produced by a heavy-duty gas turbine enginemay be greater than about 1000° F. (e.g., about 540° C.), such asbetween about 1100° F. and about 1300° F. (e.g., about 590° C. and about705° C.), while an acceptable operating range of a “hot” SCR system (anSCR system having a relatively higher operating temperature rangecompared to other SCR systems) may be between about 800° F. and about900° F. (e.g., about 425° C. and about 485° C.).

To reduce a temperature of these hot exhaust gases to the acceptableoperating range for the SCR system, the exhaust gases may be mixed withtempering air to transfer heat from the exhaust gas to the tempering airand thereby cool the exhaust gas. Generally, the amount and temperatureof tempering air therefore largely determines the amount of heat removedfrom the exhaust gas.

In an SCR system, as noted above, ammonia is reacted with NO_(x) in theexhaust gas to produce nitrogen and water. The SCR system may inject theammonia into a stream of the exhaust gas, and the resulting mixture ofammonia and exhaust gas is directed to a catalyst of the SCR system. Thesource ammonia may include “wet” ammonia, which is an aqueous solutionof ammonia, or “dry” ammonia, which is compressed or vapor ammonia thatis substantially free of water. In embodiments where the source ammoniais wet ammonia, it may be desirable to separate the ammonia from thewater in the aqueous solution. This may be accomplished by evaporatingthe ammonia away from the solution in an ammonia evaporator, whichutilizes a feed of heated air to facilitate the evaporation process.

In accordance with aspects of the present disclosure, heat from theexhaust gas may be utilized to drive the ammonia evaporation processusing one or more heat pipes. For example, it is now recognized that oneor more heat pipes positioned along an exhaust path of the exhaust gasmay conduct heat away from the exhaust gas and to one or more featuresused for ammonia evaporation. For instance, the one or more heat pipesmay impart heat to an air flow to generate heated air for the ammoniaevaporator. Additionally or alternatively, the one or more heat pipesmay impart heat directly to an aqueous solution of ammonia to generatedry ammonia for injection by the SCR system. Accordingly, in general,the heat pipes of the present disclosure may be configured to transferthermal energy from exhaust gas in an exhaust path to a heat exchangefluid (e.g., an air flow, or water within an aqueous ammonia solution)to enable the heat exchange fluid to vaporize the ammonia while coolingthe exhaust gas. The cooling of the exhaust gas may enable the DeNOxcatalyst to more effectively process the exhaust gas.

While the present disclosure may be applicable to a number of differentgas turbine systems, such as combined cycle, the embodiments describedherein may be particularly useful in simple cycle heavy-duty gas turbinesystems that produce relatively high temperature exhaust gases (e.g.,greater than 1000° F., about 540° C.). One example of a system having aconfiguration in accordance with certain aspects of the presentdisclosure is depicted in FIG. 1, which is a schematic view of anembodiment of a simple cycle gas turbine system 10. However, it shouldbe noted that the embodiments set forth herein may also be applied tocombined cycle systems.

As illustrated, the simple cycle gas turbine system 10 includes a gasturbine engine 12, which may include a heavy-duty gas turbine engine oran aero-derivative gas turbine engine. However, the present disclosuremay be particularly applicable to embodiments where the gas turbineengine 12 is a heavy-duty gas turbine engine due to the much highertemperatures of exhaust gas 14 produced in such engines. Such aspectsare discussed in further detail below.

The gas turbine system 10 may be part of a power plant, and may includea load 16 driven by the gas turbine engine 12 (e.g., a shaft 18 of thegas turbine engine 12 drivingly couples the gas turbine engine 12 to theload 16). By way of non-limiting example, the load 16 may include anelectrical generator configured to output electrical power to anelectric grid. The gas turbine engine 12 drives the load 16 byperforming a combustion process, which produces the exhaust gas 14.

The simple cycle gas turbine system 10 also includes an exhaustprocessing system 20 configured to receive the exhaust gas 14 from thegas turbine engine 12, which may enable the exhaust gas 14 to bereleased from the simple cycle gas turbine system 10. More specifically,the exhaust processing system 20 may include features configured toreduce a temperature, and/or concentration of certain products ofcombustion in the exhaust gas 14 before releasing the exhaust gas 14 viaa stack and/or to another process 22. Generally, the exhaust gas 14flows along an exhaust path 24 from the gas turbine engine 12, throughthe exhaust processing system 20, and to the stack or other process 22.

The exhaust processing system 20 includes a selective catalyticreduction (SCR) catalyst 26, which may be a part of an SCR systemconfigured to reduce a concentration of NO_(x) present within theexhaust gas 14. More particularly, the SCR catalyst 26 lowers theactivation energy for a reaction between the NO_(x) and ammonia (NH₃),which is a reducing agent, to produce nitrogen (N₂) and water (H₂O). Asnoted above, while certain types of SCR catalysts are stable atrelatively high temperatures, the exhaust gas 14 produced by the gasturbine engine 12 may still be much higher than is suitable for suchcatalysts.

To enable cooling of the exhaust gas 14 for more effective treatment ofthe exhaust gas 14 by the SCR catalyst 26, a heat pipe 28 positioned ina heat exchange relationship with the exhaust path 24 transfers thermalenergy from the exhaust gas 14 to ambient air 30. This heat transfer maybe facilitated by an ambient air heat exchanger 32 configured to place aflow of the ambient air 30 in a heat exchange relationship with the heatpipe 28. More particular arrangements of the heat pipe 28, the exhaustpath 24, and the ambient air heat exchanger 32 are described below. Inaddition, while the present disclosure refers to “ambient air,” suchdisclosures are intended to encompass treated (e.g., filtered) ambientair or untreated ambient air. Indeed, the use of untreated ambient airmay provide the advantage of reduced capital and operating costsassociated with the gas turbine system 10.

The flow of the ambient air 30 is controlled using, by way ofnon-limiting example, an air flow control system 34. The air flowcontrol system 34 may include features configured to enable monitoringand control of a flow of the ambient air 30 into the ambient air heatexchanger 32. Controlling the flow of the ambient air 30 into theambient air heat exchanger 32 may also control the temperature andpressure of heated ambient air 36 produced by heat exchange between theheat pipe 28 and the ambient air 30.

In accordance with an aspect of the present disclosure, the heatedambient air 36 facilitates ammonia vaporization in an ammonia injectionsystem 38 to generate vaporized ammonia 40. The vaporized ammonia 40, inturn, reacts with the exhaust gas 14 in the exhaust processing system 20as set forth above. The air flow control system 34 may control provisionof the heated ambient air 36 to the ammonia injection system 38 withinparticular operating ranges. For example, the air flow control system 34may adjust a flow rate, a temperature, a pressure, or any similarparameter of the heated ambient air 36 to within a particular operatingrange depending on characteristics of the heated ambient air 36 suitableto achieve a level of ammonia vaporization appropriate for the exhaustprocessing system 20. The air flow control system 34 may be a part of alarger control system that is centrally located or distributed, asdescribed in further detail below.

In situations where the ammonia injection system 38 does not necessarilyneed the total amount of the heated ambient air 36 exiting the ambientair heat exchanger 32, the air flow control system 34 may direct atleast a portion of the heated ambient air 36 to a vent or other process42. In this regard, the air flow control system 34 may control a splitof the heated ambient air 36 between a first heated air flow path 44leading to the ammonia injection system 38 and a second heated air flowpath 46 leading to the vent or other process 42.

A side elevational view of an embodiment of the simple cycle gas turbinesystem 10 is shown in FIG. 2. The gas turbine engine 12 may generallypower the gas turbine system 10, and includes one or more combustors 50in which a fuel 52 and compressed oxidant 54 (e.g., compressed air) aremixed and undergo combustion. Other streams may also be present in thecombustor to adjust combustion parameters as appropriate (e.g., exhaustgas diluent). Combustion products 56 generated in the one or morecombustors 50 flow to a turbine 58, which extracts work from thecombustion products 56 to rotate the shaft 18 of the gas turbine engine12. The turbine 58 drives compression stages of an oxidant compressor 60via the rotation of the shaft 18. Staged compression within the oxidantcompressor 60 creates a pressure gradient that draws in ambient air 30to continue the compression and combustion cycle.

The combustion products 56 exit the turbine 58 as the exhaust gas 14,which is directed into an exhaust duct assembly 62 fluidly coupled to anoutlet 64 of the turbine 58. The exhaust duct assembly 62 may includesegments fluidly coupled to one another, or may include a singlecontinuous duct. In certain embodiments, the exhaust duct assembly 62may be segmented to allow for ready maintenance and replacement asappropriate.

The exhaust duct assembly 62 includes an exhaust inlet 66 configured toreceive the exhaust gas 14 from the gas turbine engine 12, and anexhaust gas outlet 68 in the form of a stack 70. Generally, features ofthe exhaust processing system 20 are located within the exhaust ductassembly 62 along the exhaust path 24 and are configured to sequentiallyprocess the exhaust gas 14 as the exhaust gas flows from the exhaustinlet 66 to the exhaust outlet 68. The processing may includeencouraging turbulent flow of the exhaust gas 14 (which facilitates heatexchange), direct or indirect heat exchange, and catalytic byproductremoval, among others.

In the illustrated embodiment, such features include, but are notlimited to, an ammonia injection grid 72 configured to inject thevaporized ammonia 40 into the exhaust path 24, the SCR catalyst 26, anda plurality of heat pipes 74 having respective first portions 76 (e.g.,first ends) positioned along the exhaust path 24 upstream of the SCRcatalyst 26. The heat pipe 28 described above with respect to FIG. 1 maybe one heat pipe of the plurality of heat pipes 74 or, in otherembodiments, the heat pipe 28 may be the only heat pipe positioned alongthe exhaust path 24.

The respective first portions 76 of the plurality of heat pipes 74 areillustrated as being positioned between the ammonia injection grid 72and the SCR catalyst 26. This configuration may facilitate mixing of theexhaust gas 14 and the vaporized ammonia 40 by encouraging turbulentflow. Facilitating mixing in this manner may encourage homogeneity ofthe vaporized ammonia 40 and the exhaust gas 14 from both acompositional and thermal standpoint. However, the plurality of heatpipes 74 may have their respective first portions 76 positioned in anyone or a combination of different locations along the exhaust flow path24, including upstream and/or downstream of the ammonia injection grid72.

During operation of the simple cycle gas turbine system 10, the exhaustgas 14 flows along the exhaust path 24 in a bulk flow direction 78. Thefirst portions 76 of the plurality of heat pipes 74, being orientedcrosswise relative to the bulk flow direction 78, contact the exhaustgas 14 (and vaporized ammonia 40, in the illustrated embodiment) andreceive thermal energy from (and cool) the exhaust gas 14. Accordingly,the first portions 76 of the plurality of heat pipes 74 correspond to a“hot” side or end of the plurality of heat pipes 74.

In one non-limiting example, a temperature of the exhaust gas 14entering the exhaust duct assembly 62 from the gas turbine engine 12 isbetween about 1000° F. (about 540° C.) and about 1200° F. (about 650°C.). This temperature range may be higher than suitable for the SCRcatalyst 26. The plurality of heat pipes 74 reduces the temperature ofthe exhaust gas 14 to between about 800° F. (about 430° C.) and about900° F. (about 480° C.) before the exhaust gas 14 reaches the SCRcatalyst 26, which may be more suitable for the SCR catalyst 26. Thatis, the SCR catalyst 26 may be more efficient in catalyzing the reactionbetween the vaporized ammonia 40 and the NO_(x) in the exhaust gas 14 atsuch temperatures.

By way of non-limiting example, the plurality of heat pipes 74 may bearranged in rows of individual heat pipes 28 (e.g., substantiallyaligned along the bulk flow direction 78), columns of individual heatpipes 28 (e.g., substantially aligned crosswise relative to the bulkflow direction 78), staggered rows and columns of individual heat pipes28, or any combination thereof. Thus, any suitable arrangement of theplurality of heat pipes 74 may be utilized that enables the firstportions 76 to contact the exhaust gas 14.

Each heat pipe 28 of the plurality of heat pipes 74 is configured torapidly conduct thermal energy from its respective first portion 76 (hotside or hot end) to a respective second portion 80 or end, which is a“cold” side or end of the heat pipe 28. It is presently recognized thatthe second portions 80 of the plurality of heat pipes 74 may be placedin thermal communication (e.g., a heat exchange relationship) with oneor more fluids (e.g., a heat exchange fluid) to integrate cooling andheating processes utilized in the exhaust processing system 20. In theillustrated embodiment of FIG. 2, the cooling process involves coolingof the exhaust gas 14 and vaporized ammonia 40, and the heating processinvolves heating a fluid to produce, either directly or indirectly, thevaporized ammonia 40. Further, the embodiment depicted in FIG. 2 is notlimited to the specific heat exchange relationship shown.

For example, in one embodiment, a first set of the plurality of heatpipes 74 may have respective second portions 80 positioned in a heatexchange relationship with the ambient air 30 (e.g., a first flow pathof a heat exchange fluid). Further, a second set of the plurality ofheat pipes 74 may have respective second portions 80 in a separate heatexchange relationship with the ambient air 30 (e.g., a second flow pathof the heat exchange fluid). The second flow path may be separate fromand arranged in parallel with respect to the first flow path, and maylead to the same or different destinations (e.g., be used for the sameor different purposes).

The one or more fluids may be capable of receiving thermal energy fromthe second portions 80 of the plurality of heat pipes 74 (e.g.,rejecting heat from the second portions 80 of the plurality of heatpipes 74). In the illustrated embodiment, the heat exchange fluid isambient air 30 taken into the ambient air heat exchanger 32. However,other heat exchange fluids may be utilized. For example, the heatexchange fluid may be water in the aqueous ammonia subject tovaporization.

The air flow control 34 described with respect to FIG. 1 may include, asillustrated, a heated air flow control device 82 configured tocontrollably close or open a heated air path 84 (e.g., a heated airconduit) coupling an outlet 86 of the ambient air heat exchanger 32 to aheated air motivator 88. That is, the heated air flow control device 82is configured to at least partially control a flow of the heated ambientair 36 to the heated air motivator 88. By way of non-limiting example,the heated air flow control device 82 may include a damper 90 coupled toan actuation mechanism 92. The actuation mechanism 92 may becommunicatively coupled to an exhaust processing control system 94configured to control operation of the damper 90 via the actuationmechanism 92. In certain embodiments, the heated air flow control device82 may include a plurality of flow control devices.

The exhaust processing control system 94 may also regulate otheroperational aspects of the exhaust processing system 20. For example,the exhaust processing control system 94 is communicatively coupled to avariety of components that facilitate regulation of a flow rate,temperature, pressure, and so forth, of various fluids used to achievesuitable processing of the exhaust gas 14.

The exhaust processing control system 94 may be implemented on anysuitable programmable architecture, such as an architecture includingone or more processors 96 and one or more memory 98. Once programmed,the exhaust processing control system 94 may be considered to constitutea specially-configured device that is configured to control specificaspects relating to the exhaust processing system 20 based at least onalgorithmic structure associated with its programming. In this way, theexhaust processing control system 94 be configured to perform certainfunctions, and these functions should be considered to denote a specificalgorithmic structure of the exhaust processing control system 94, forexample a structure associated with the one or more processors 96 andone or more memory 98.

By way of non-limiting example, the exhaust processing control system 94may include one or more application specific integrated circuits(ASICs), one or more field programmable gate arrays (FPGAs), one or moregeneral purpose processors, or any combination thereof. Additionally,the memory 98 storing instructions executed by processors 96 of theexhaust processing control system 94 may include, but are not limitedto, volatile memory, such as random access memory (RAM), and/ornon-volatile memory, such as read-only memory (ROM), optical drives,hard disc drives, or solid-state drives. Further, the exhaust processingcontrol system 94 may be implemented as a part of a larger controlsystem (e.g., a gas turbine control system), and/or as a variety ofcontrol devices and/or subsystems distributed throughout simple cyclegas turbine system 10 (e.g., a distributed control system). The controldevices and/or subsystems, therefore, may include any one or acombination of the processing and memory circuitry configurations notedabove. Additionally, the exhaust processing control system 94 willgenerally include various input devices, and may include a userinterface in the form of a display, or in the form of a connector thatis accessible through wired or wireless connection with a computingdevice of the user.

The exhaust processing control system 94 is also communicatively coupledto the heated air motivator 88. The heated air motivator 88 isconfigured to motivate the heated ambient air 36 to the ammoniainjection system 38, and may include a blower, fan, pump, compressor, orsimilar device. The heated air motivator 88 may create a pressuregradient between the ambient air heat exchanger 32 and its outlet 96,which functions to draw the ambient air 30 into the ambient air heatexchanger 32. Accordingly, the operation of the heated air motivator 88may be controlled to affect a residence time of ambient air 30 in theambient air heat exchanger 32, which in turn affects a temperature andpressure of the heated ambient air 36.

Additional features may be present upstream of the heated air motivator88 to process the ambient air 30 and/or the heated ambient air 36. Forexample, one or more filters, silencers, and so forth, may be positionedupstream of an inlet 100 of the ambient air heat exchanger 32, withinthe ambient air heat exchanger 32, or along the heated air flow path 84,or any combination.

Again, the heated air motivator 88 directs the heated ambient air 36 tothe ammonia injection system 38 for ammonia vaporization. Moreparticularly, in the illustrated embodiment, the heated ambient air 36is directed into an ammonia evaporator 102 of the ammonia injectionsystem 38 through a heated air inlet 104. The ammonia evaporator 102also includes an ammonia inlet 106 configured to receive ammonia (e.g.,aqueous ammonia 107) from an ammonia source 108, and a vaporized ammoniaoutlet 110 fluidly coupled to the ammonia injection grid 72 by avaporized ammonia flow path 111 (e.g., a vaporized ammonia conduit).

In accordance with present embodiments, vaporization of the aqueousammonia 107 (ammonium hydroxide) generates the vaporized ammonia 40. Theaqueous ammonia 107 may be held in a storage vessel 110 configured tostore the aqueous ammonia 107 under controlled conditions (e.g., closedto the ambient environment). The storage vessel 110 may include a tankor similar vessel that allows the aqueous ammonia 107 to be controllablywithdrawn.

To allow for such control, the ammonia injection system 38 may includevarious flow control and motivation features positioned along an aqueousammonia flow path 112 coupling an outlet 114 of the storage vessel 110to the aqueous ammonia inlet 106 of the ammonia evaporator 102. In theillustrated embodiment, an ammonia motivator 116 positioned along theaqueous ammonia flow path 112 is configured to create a pressuregradient between the ammonia source 108 and the ammonia evaporator 102.The pressure gradient causes the aqueous ammonia 107 to be withdrawnfrom the storage vessel 110 and motivated toward the ammonia evaporator102. The ammonia motivator 116 may include a pump or similar featurecapable of motivating a fluid having properties of the aqueous ammonia107 in a suitable manner. As an example, the aqueous ammonia 107 held inthe storage vessel 110 may include between about 15% and about 20% byvolume or by weight ammonia (NH₃), with the remainder being water. Inone embodiment, the aqueous ammonia 107 is a 19% by weight solution ofammonia in water.

An ammonia flow control unit 118 positioned along the aqueous ammoniaflow path 112 may further adjust the flow of the aqueous ammonia 107,for example by controllably restricting the size of the flow path 112(e.g., controllably closing or opening an orifice). The ammonia flowcontrol unit 118 may be positioned downstream of the ammonia motivator116 as shown, or may be positioned upstream of it (between the ammoniasource 108 and the ammonia motivator 116).

The exhaust processing control system 94 is shown as beingcommunicatively coupled to the ammonia motivator 116 and the ammoniaflow control unit 118. In accordance with the illustrated embodiment,the exhaust processing control system 94 may control one or moreoperating parameters of the ammonia motivator 116 and/or the ammoniaflow control unit 118 to control the amount of aqueous ammonia 107provided to the ammonia evaporator 102 over time.

The ammonia evaporator 102 is schematically depicted as having aninjection nozzle 120 fluidly coupled to the aqueous ammonia flow path112. The injection nozzle 120 may be configured to inject a spray of theaqueous ammonia 107 into the ammonia evaporator 102 to encourageatomization. The aqueous ammonia 107 is also brought into heat exchangewith the heated ambient air 36, which further encourages evaporation ofthe aqueous ammonia 107 to produce the vaporized ammonia 40. The heatexchange between the aqueous ammonia 107 and the heated ambient air 36may be through direct contact of their associated flows, or indirect byway of heat exchange features within the ammonia evaporator 102. Thevaporized ammonia 40 may be discharged as an overhead vapor through thevaporized ammonia outlet 110.

In the illustrated embodiment, the vaporized ammonia 40 is provided tothe ammonia injection grid 72 via the vaporized ammonia flow path 111.The ammonia injection grid 72 includes a plurality of spray injectors122 configured to introduce the vaporized ammonia 40 into the exhaustpath 24. The plurality of spray injectors 122, as shown, may have thesame axial position along the flow direction 78 but different radialpositions with respect to the exhaust duct assembly 62.

The amount of vaporized ammonia 40 introduced into the exhaust path 24may be controlled by the exhaust processing control system 94 to achievea particular objective. For example, the amount of vaporized ammonia 40introduced into the exhaust path 24 may be controlled over time toachieve a desired amount of NO_(x) reduction within the exhaust gas 14(e.g., maximum NO_(x) reduction, reduction of NO_(x) to a mandatedlevel). By way of non-limiting example, the amount of vaporized ammonia40 introduced into the exhaust path 24 may be determined or otherwisecontrolled by the exhaust processing control system 94 a function ofvarious parameters, such as the amount of exhaust gas 14 flowing throughthe exhaust path 24, a composition of the exhaust gas 14 (e.g., thelevel of NO_(x) in the exhaust gas 14), activity of the SCR catalyst 26,and so forth.

The amount of vaporized ammonia 40 used for NO_(x) reduction may, inturn, determine how the exhaust processing control system 94 controlsintake and heating of the ambient air 30 in the ambient air heatexchanger 32. By way of non-limiting example, the exhaust processingcontrol system 94 may control a temperature of the heated ambient air 36and a flow rate of the heated ambient air 36 to respective levels thatare appropriate to produce suitable amounts of the vaporized ammonia 40(e.g., as a function of time, as a function of exhaust gas composition,or a combination).

The manner in which the exhaust processing control system 94 may monitorand control elements of the system 10 may be further appreciated withrespect to FIG. 3, which is a schematic side view of an embodiment ofthe gas turbine system 10. More specifically, the embodiment of the gasturbine system 10 includes one or more exhaust sensors 130 positionedalong the exhaust duct 62 at various positions in the exhaust flowdirection 72. The one or more exhaust sensors 130 may be communicativelycoupled to the exhaust processing control system 94 to enable monitoringof one or more parameters of the exhaust gas 14 as it flows through theexhaust duct 62. By way of non-limiting example, the exhaust sensors 130may enable monitoring of temperature, pressure, oxygen levels, NO_(x)levels, CO levels, and/or similar parameters.

In the illustrated embodiment, for example, the exhaust sensors 130 maybe configured to monitor one or more parameters of the exhaust gas 14upstream of the ammonia injection grid 72, between the ammonia injectiongrid 72 and the plurality of heat pipes 74, between the plurality ofheat pipes 74 and the SCR catalyst 26, and/or downstream of the SCRcatalyst 26. As a more specific example, the exhaust gas 14 temperaturemay be monitored upstream of the SCR catalyst 26 to enable the exhaustprocessing control system 94 to determine appropriate flows andtemperatures for the vaporized ammonia 40, the ambient air 30, theheated ambient air 36, and so forth. A first of the exhaust sensors 130positioned upstream of the ammonia injection grid 72 may monitor atemperature of the exhaust gas 14 before mixing with the vaporizedammonia 40, while a second of the exhaust sensors 130 positioned betweenthe ammonia injection grid 72 and the plurality of heat pipes 74 maymonitor a temperature of a mixture of the exhaust gas 14 and thevaporized ammonia 40. Feedback relating to cooling of this mixture bythe plurality of heat pipes 74 may be obtained by a third of the exhaustsensors 130 positioned between the plurality of heat pipes 74 and theSCR catalyst 26. Additionally or alternatively, the exhaust gascomposition (e.g., NO_(x) levels) of treated exhaust gas 132 downstreamof the SCR catalyst 26 may be monitored to determine appropriate flowrates and temperatures for the vaporized ammonia 40, the ambient air 30,the heated ambient air 36, and so forth.

The exhaust processing control system 94 is also communicatively coupledto features that enable the exhaust processing control system 94 tomonitor and control such flows and temperatures. For instance, anambient air sensor 134 may be a temperature sensor configured to enablethe exhaust processing control system 94 to monitor a temperature of theambient air 30. Based at least on this information, the exhaustprocessing control system 94 may determine the extent to which theambient air 30 should be heated within the ambient air heat exchanger32. This may be at least partially accomplished by controlling a flowrate of the ambient air 30 using one or more ambient air flow controldevices 136 (e.g., including a fan and/or baffle) positioned upstream ofthe ambient air heat exchanger 32 via associated actuators 138 and/orusing the flow control devices 88, 90 downstream of the ambient air heatexchanger 32.

The ambient air sensor 134 is positioned upstream of the ambient airheat exchanger 32 (e.g., upstream along a flow path of a heat exchangefluid), which may provide feed forward information to the exhaustprocessing control system 94. Indeed, the exhaust processing controlsystem 94 may include one or more air flow control modules 140 (e.g.,code implemented in software) configured to provide air flow controlusing the feed forward information and, additionally or alternatively,feedback information from a heated ambient air sensor 142 positioneddownstream of the ambient air heat exchanger 32.

The exhaust processing control system 94 may also be communicativelycoupled to features of the ammonia injection system 38, and may includeone or more ammonia injection control modules 144 (e.g., codeimplemented in software) configured to provide control over operationalaspects of the ammonia injection system 38. For example, the one or moreammonia injection control modules 144 may control the rate at which theammonia injection system 38 produces the vaporized ammonia 40, atemperature of the vaporized ammonia 40, or similar parameters. As anexample, the control may be performed based on a target NO_(x) level forthe treated exhaust gas 132, which may be a feed forward input, as wellas feedback obtained from the one or more exhaust sensors 130, such as afourth of the exhaust sensors positioned downstream of the SCR catalyst26. The feedback information may include, as one example, a measuredlevel of NO_(x) within the treated exhaust gas 132.

The exhaust processing control system 94 may monitor parameters relatingto the ammonia injection system 38, such as a temperature of the aqueousammonia 107, flow rates of the aqueous ammonia 107 through the ammoniainjection system 38, and so forth, via communication with one or moreammonia sensors 146. The exhaust processing control system 94 may usefeedback generated by the one or more ammonia sensors 146 as a controlinput for the overall control of the injection of vaporized ammonia 40into the exhaust duct 62.

Again, embodiments of the present disclosure may utilize one or moreheat pipes 28 (e.g., the plurality of heat pipes 74) to cool the exhaustgas 14 within the exhaust duct 62. In this regard, while the illustratedembodiments of FIGS. 2 and 3 depict the heat pipe 28 (or pluralitythereof) as being positioned between the ammonia injection grid 72 andthe SCR catalyst 26, the present disclosure is not necessarily limitedto this configuration. Indeed, embodiments of the present disclosure mayuse one or more heat pipes 28 positioned at any point along the exhaustflow direction 78 upstream of the SCR catalyst 26. Thus, certainembodiments of the gas turbine system 10 may include one or more heatpipes 28 positioned upstream of the ammonia injection grid 72, either inaddition to or as an alternative to one or more heat pipes 28 positionedbetween the ammonia injection grid 72 and the SCR catalyst 26.

A non-limiting example embodiment of the thermal configuration the heatpipe 28 or plurality of heat pipes 74 is depicted in FIG. 4. Morespecifically, a cross-sectional elevation view of the heat pipe 28 isshown in FIG. 4. The heat pipe 28 includes an exterior casing 160defining an outer surface of the heat pipe 28. An absorbent wick 162 isdisposed inside of the exterior casing 160 and surrounds a vapor cavity164. A working fluid 166 such as a metal (e.g., sodium), a hydrocarbon,ammonia, or water, is disposed in the vapor cavity 164. The firstportion 76 of the heat pipe 28 (the hot side or hot end) is disposedsuch that the exhaust gas 14 flows across the first portion 76, whilethe second portion 80 (the cool side or cool end) is positioned in aheat exchange relationship with a heat exchange fluid along a flow pathof the heat exchange fluid. As illustrated, the heat exchange fluid mayinclude the ambient air 30 as shown in FIGS. 2 and 3, or may includewater present within the aqueous ammonia 107, which his described infurther detail below with respect to FIG. 5.

At the first portion 76, thermal energy from the exhaust gas 14transfers to the heat pipe 28, causing the working fluid 166 in the wick162 at the first portion 76 to evaporate and migrate into the vaporcavity 164. This evaporation may also cause some evaporative cooling ofthe first portion 76 to thereby additionally cool the exhaust gas 14 andproduce a cooled exhaust gas 168.

The vapor migrates to the second portion 80 along the vapor cavity 164.The vapor condenses at the second portion 80 and is absorbed by the wick162, releasing the thermal energy to the heat exchange fluid in a heatexchanger (e.g., the ambient air heat exchanger 32 or the ammoniaevaporator 102). The working fluid 166 migrates via the wick 162 to thefirst portion 76.

Additionally or alternatively, one or more of the heat pipes 28 may haveother configurations. By way of non-limiting example, one or more of theheat pipes 28 may be a solid state heat pipe in which thermal energy ofthe exhaust gas 14 is absorbed by a highly thermally conductive solidmedium disposed within the casing 160. In such embodiments, thetemperature difference between the first and second portions 76, 80 maycause thermal energy migration to enable the heat pipe 28 to heat theambient air 30 or directly vaporize the ammonia.

As set forth above, in addition to or in lieu of heating air, the heatpipes 28 may be configured to directly heat and vaporize the aqueousammonia 107. FIG. 5 is a schematic elevational view of an exampleembodiment having this configuration. In the illustrated embodiment, theheat pipe 28 or the plurality of heat pipes 74 have their respectivesecond portions 80 positioned in the ammonia evaporator 102. In thisembodiment, the heat exchange fluid that is heated to effect ammoniavaporization may include water within the aqueous ammonia 107. Similarto the embodiment in FIG. 2, the exhaust processing control system 94may control the flow of the aqueous ammonia 107 to the ammoniaevaporator 102 using one or more ammonia flow control devices such asthe ammonia motivator 116 and/or the ammonia flow control unit 118 andassociated actuators 180.

While the ammonia motivator 116 and/or the ammonia flow control unit 118may be positioned upstream of the ammonia evaporator 102, one or moreevaporated ammonia flow control devices 182 and associated actuators 184may be positioned along the evaporated ammonia flow path 111 downstreamof the ammonia evaporator 102. The exhaust processing control system 94may be in communication with the one or more evaporated ammonia flowcontrol devices 182 and associated actuators 184 to enable additionalcontrol of evaporated ammonia injection via the ammonia injection grid72. The exhaust processing control system 94 of FIG. 5 may havesubstantially the same configuration as set forth above with respect toFIG. 3, but may adjust ammonia flow as the primary and/or sole controlparameter in response to feedback from the exhaust sensors 130, theammonia sensors 146, and so forth.

Additional or alternative configurations for the system 10 of FIG. 5 arealso possible. For example, rather than causing direct and totalvaporization of the aqueous ammonia 107, the heat pipe 28 may be used topre-heat the aqueous ammonia 107 to reduce reliance on other sources ofheat. For example, the heat pipe 28 may be used to pre-heat the aqueousammonia 107 to enable easier ammonia evaporation using heated ambientair generated by electric air heating of ambient air. This may reducereliance on electrical energy to drive electric heaters while enablingtunable control of the final evaporated ammonia temperature usingadditional control mechanisms (e.g., electric heaters).

Indeed, any of the embodiments described herein may be used in lieu ofor in addition to other independent heat exchange fluid flow paths,which may be independent and parallel to the flow paths describedherein. As a more specific example, certain embodiments, such as theembodiment of FIG. 3, may also utilize an additional independent andparallel flow path for the ambient air 30 that flows the ambient air 30over electric heaters to enable the use of an additional temperaturecontrol mechanism for ammonia evaporation.

Technical effects of the invention include the heat integration ofexhaust gas release from a gas turbine engine with ammonia evaporationin an exhaust processing system that reduces NO_(x) in the exhaust gas.The heat integration may be accomplished using one or more heat pipes,where the one or more heat pipes are transfer thermal energy from thegas turbine flue gas (the exhaust gas) and to a heat exchange mediumthat is ultimately used for ammonia vaporization. This may reducereliance on other forms of energy that would otherwise be required forammonia evaporation, thereby enhancing efficiency of the exhaust gastreatment process.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

1. A gas turbine system, comprising: an exhaust processing systemfluidly coupled to an outlet of a turbine of a gas turbine engine, theexhaust processing system being configured to receive an exhaust gashaving products of combustion generated by the gas turbine engine, andto process the exhaust gas before the exhaust gas exits the gas turbinesystem; an exhaust path of the exhaust processing system configured toflow the exhaust gas through the exhaust processing system; an ammoniainjection system having a source of ammonia and configured to introducevaporized ammonia into the exhaust path; and a heat pipe having a firstportion positioned within the exhaust path and a second portionpositioned in a heat exchange relationship with a flow path of a heatexchange fluid used in the ammonia injection system, and wherein theheat pipe is configured to transfer thermal energy from exhaust gas inthe exhaust path to the heat exchange fluid to enable the heat exchangefluid to vaporize the ammonia while cooling the exhaust gas to enablethe exhaust processing system to more effectively process the exhaustgas.
 2. The system of claim 1, wherein the second portion of the heatpipe is positioned along an ambient air flow path leading to an ammoniaevaporator of the ammonia injection system.
 3. The system of claim 2,wherein the ammonia evaporator is configured to receive a flow of heatedambient air and place the heated ambient air in heat exchange withaqueous ammonia to generate vaporized ammonia.
 4. The system of claim 3,comprising a flow control device positioned along the ambient air flowpath and configured to control a flow of ambient air over the secondportion of the heat pipe.
 5. The system of claim 4, comprising acontroller communicatively coupled to the flow control device configuredto adjust the flow control device to adjust a temperature of the heatedambient air.
 6. The system of claim 3, comprising an ammonia injectiongrid positioned along the exhaust path and fluidly coupled to theammonia evaporator, wherein the ammonia injection grid is configured toreceive the vaporized ammonia from the ammonia evaporator and to injectthe vaporized ammonia into the exhaust path.
 7. The system of claim 6,wherein the first portion of the heat pipe is positioned downstream ofthe ammonia injection grid.
 8. The system of claim 1, wherein the firstportion of the heat pipe is positioned upstream a selective catalyticreduction (SCR) catalyst of the exhaust processing system configured toreduce a concentration of nitrogen oxides (NO_(x)) in the exhaust gas.9. The system of claim 1, wherein the heat pipe is one of a plurality ofheat pipes having respective first portions positioned within theexhaust path.
 10. The system of claim 9, wherein less than all the heatpipes of the plurality of heat pipes have respective second portionspositioned in the heat exchange relationship with the flow path of theheat exchange fluid.
 11. The system of claim 9, wherein a first set ofthe plurality of heat pipes have respective second portions positionedin the heat exchange relationship with the flow path of the heatexchange fluid, and wherein a second set of the plurality of heat pipeshave respective second portions in a separate heat exchange relationshipwith an additional flow path of the heat exchange fluid, wherein theadditional flow path is separate from and arranged in parallel withrespect to the flow path.
 12. The system of claim 9, wherein all heatpipes of the plurality of heat pipes have respective second portionspositioned in the heat exchange relationship with the flow path of theheat exchange fluid.
 13. The system of claim 1, wherein the heat pipe isconfigured to transfer the thermal energy from the exhaust gas and tothe heat exchange fluid using phase change of a fluid contained withinthe heat pipe.
 14. The system of claim 1, wherein the heat pipe has avapor cavity, a wick surrounding the vapor cavity, and a fluid, andwherein the heat pipe is configured to receive thermal energy from theexhaust gas at the first portion and to use the thermal energy toevaporate the fluid to cause the fluid to move from the wick and intothe vapor cavity to thereby evaporatively cool the first portion, andwherein the heat pipe is configured to transfer thermal energy to theheat exchange fluid at the second portion to cause the fluid to cool andbe re-absorbed by the wick.
 15. The system of claim 1, wherein thesource of ammonia is a storage tank holding aqueous ammonia, and whereinthe flow path of the heat exchange fluid is configured to flow theaqueous ammonia, the heat exchange fluid being water in the aqueousammonia such that the heat pipe is configured to directly evaporate theammonia.
 16. A system, comprising: a heat pipe having a first portionpositioned within an exhaust path of a gas turbine exhaust processingsystem and a second portion positioned in a heat exchange relationshipwith a flow path of a heat exchange fluid; and wherein the flow path ofthe heat exchange fluid includes an ammonia evaporator configured toevaporate ammonia received from an ammonia source, and wherein the heatpipe is configured to transfer thermal energy from exhaust gas in theexhaust path to the heat exchange fluid to enable the heat exchangefluid to vaporize the ammonia while cooling the exhaust gas to enablethe gas turbine exhaust processing system to more effectively processthe exhaust gas.
 17. The system of claim 16, wherein the heat pipe isconfigured to transfer the thermal energy from the exhaust gas and tothe heat exchange fluid using phase change of a fluid contained withinthe heat pipe.
 18. The system of claim 16, comprising a plurality ofheat pipes including the heat pipe, wherein the gas turbine exhaustprocessing system includes a selective catalytic reduction (SCR)catalyst configured to reduce a concentration of NO_(x) within theexhaust gas, and the plurality of heat pipes is configured to reduce atemperature of the exhaust gas from a first temperature to a secondtemperature, wherein the SCR catalyst has a better catalytic activity atthe second temperature compared to the first temperature.
 19. The systemof claim 16, wherein the ammonia source includes a source of aqueousammonia, and the heat exchange fluid is air, or is water of the aqueousammonia.
 20. A gas turbine system, comprising: a gas turbine engineconfigured to combust a mixture of fuel and an oxidant and to releaseexhaust gas resulting from the combustion; an exhaust processing systemhaving an exhaust duct fluidly coupled to an outlet of a turbine of thegas turbine engine, the exhaust duct being configured to receive theexhaust gas released by the gas turbine engine, wherein the exhaustprocessing system is configured to process the exhaust gas using aselective catalytic reduction (SCR) catalyst to reduce NO_(x) in theexhaust gas before the exhaust gas exits the gas turbine system; anexhaust path of the exhaust processing system configured to flow theexhaust gas through the exhaust processing system; an ammonia injectionsystem having an ammonia evaporator configured to receive aqueousammonia from an ammonia source and to vaporize ammonia in the aqueousammonia and to enable the ammonia injection system to introducevaporized ammonia into the exhaust path; and a plurality of heat pipesconfigured to receive thermal energy from exhaust gas in the exhaustduct to cool the exhaust gas before the exhaust gas reaches the SCRcatalyst and to transfer the thermal energy to a heat exchange fluidused in the ammonia evaporator to vaporize the ammonia.